1. Field of the Invention
Exemplary aspects of the present invention relate to a rotary body driver and an image forming apparatus, and more particularly, to a rotary body driver for driving a rotary body and an image forming apparatus incorporating the rotary body driver.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of a photoconductor; an optical writer emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a development device supplies toner to the electrostatic latent image formed on the photoconductor to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the photoconductor onto a recording medium or is indirectly transferred from the photoconductor onto a recording medium via an intermediate transfer belt; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
Since the electrostatic latent image and the resultant toner image are formed on the photoconductor as it rotates and the toner image is transferred from the photoconductor onto the intermediate transfer belt as they rotate, the photoconductor and the intermediate transfer belt are required to rotate at a precise, predetermined rotation speed. Otherwise, a faulty toner image, such as a jittered image or a banded image, is formed due to variation in the rotation speed of the photoconductor and the intermediate transfer belt (hereinafter referred to as a rotary body).
To address this requirement, a rotary body driver employing a planetary gear transmission is proposed to drive and rotate the rotary body at a predetermined rotation speed precisely. For example, the planetary gear transmission is connected to a motor and a tubular rotary body to transmit a driving force generated by the motor to the rotary body. Specifically, the planetary gear transmission includes a sun gear coaxially connected to an output shaft of the motor. A plurality of planet gears rotatably supported by a carrier surrounds the sun gear in such a manner that the planet gears are meshed with the sun gear and an outer gear encircling the planet gears.
As the motor rotates, a driving force of the motor is transmitted to the sun gear. Accordingly, the planet gears meshed with the sun gear and the outer gear rotate and at the same time revolve about the sun gear. Consequently, the carrier supporting the planet gears revolves about the sun gear, rotating the rotary body coaxially connected to the carrier. That is, the carrier serves as an output shaft of the planetary gear transmission and a rotary body shaft of the rotary body, thus transmitting the driving force to the rotary body. The planetary gear transmission transmits the driving force generated by the motor rotating at a predetermined rotation speed range with minimized speed variation by speed reduction gearing at an increased reduction ratio, thus minimizing variation in the rotation speed of the rotary body.
At the same time, there is a growing demand for industrial products that save resources, i.e., are lightweight, use fewer, more durable parts that are recyclable, and consume less energy during manufacture and operation.
In order to meet such demand, the rotary body driver should be lightweight as well. For example, if all the major components of the planetary gear transmission of the rotary body driver are made of metal, the weight of the planetary gear transmission may increase. Conversely, if all the major components of the planetary gear transmission are made of resin, the weight of the planetary gear transmission may decrease. However, since resin has load duration smaller than that of metal, the resin carrier of the planetary gear transmission that transmits the driving force from the motor to the rotary body may not endure against load imposed by the rotary body and may be subject to breakage.
Accordingly, there is a need for a rotary body driver that is both lightweight and durable against load.